[en] The developed model in this work is similar to a classical model of a conventional boiler (combination of a combustion chamber and a water-flue gas heat exchanger) to which a model of a heat exchanger for condensation has been added. This latter has been simulated by a cooling coil divided into several elements The developed model has been applied on a condensing whose nominal useful power is 24.6 KW. After the determination of the nominal parameters, tests have been performed to validate the model in different working conditions of the boiler. The two main parameters whose influence has been investigated are : the return water temperature and the overall excess air.